In recent years, techniques to identify the colors of images are attracting attention in the field of image processing. For example, Patent Document 1 discloses a technique to generate chrominance information of pixels composing an image captured by a digital camera on a pixel-by-pixel basis, and extract a subject having a specific hue based on the generated chrominance information. The technique disclosed in Patent Document 1 is useful in autofocus and exposure adjustment in a digital camera.
Patent Document 2 discloses a technique to generate RGB signals from an image captured by an onboard camera, and detect a yellow portion in the captured image based on the generated RGB signals. Specifically, according to the technique disclosed in Patent Document 2, pixels that satisfy the following conditions are specified and extracted as a yellow portion: the R value is larger than the B value, the G value is larger than the B value, and a value obtained by subtracting the B value from the R value is larger than a set value. The technique disclosed in Patent Document 2 can be used in parking assistance when parking lines are painted in yellow, and in detection of road surface markings that are painted in yellow.
It is expected that the use of such techniques to extract a specific color from captured images can realize easy detection of buildings, facilities, people in distress, and so forth from, for example, aerial photographs or satellite photographs.